The present invention relates to the remote detection of trace contaminants in a target area and, more particularly, to the detection of explosives by remote observation of the effect of explosive-signature compounds on the fluorescence of sensor particles applied to a suspect mined area.
Currently, there are no reliable methods for the remote detection of buried landmines and/or antipersonnel minefields. Geophysical sensors for landmine detection, such as electromagnetic induction sensors, magnetometers, and radar can exhibit high probabilities of detection but their performance is often limited by high false alarm rates due to xe2x80x9cclutterxe2x80x9d from objects with physical properties similar to those of the target mines.
The presence of explosive compounds in or above the soil can provide a useful discriminating signature for detection of buried mines or other unexploded ordnance. However, neither trace chemical detection methods (xe2x80x9csniffersxe2x80x9d) nor bulk methods (e.g., nuclear quadrupole resonance) are capable of standoff detection at ranges greater than a few meters. Additionally, trace chemical methods are limited by environmental fate and transport of explosive compounds in the minefield environment. The concentration of landmine signature compounds like trinitrotoluene (TNT) and dinitrotoluene (DNT) adsorbed on soils has been found to far exceed the equilibrium vapor concentration, while most of the transport of these explosives through soil occurs in the aqueous phase. M. Ia Grone et al., SPIE 3710, 401 (1999). The maximum measured concentrations of nitroaromatic compounds in surface soils above buried landmines have been reported to be as high as a part per million (about 1 mg/kg). However, laboratory measurements of vapor concentrations above similarly contaminated soils are many orders of magnitude lower. Thus, phase partitioning favors detection of adsorbed or aqueous compounds. Furthermore, the difficulty in detecting vapor fromadsorbed explosives in the soil, in conjunction with the requirement for rapid sampling and analysis to maintain forward progress of a sensor, places severe requirements on the performance of vapor sensors. In particular, extremely low mass limits of detection are required for a trace chemical sensor to respond to the vapor over a buried landmine.
Significant investment has been made in developing remote optical methods (optical absorption and/or fluorescence light detection and ranging) for the detection of chemical- and bio-warfare agents. However, no similar methods currently exist for the remote detection of minefields, due to the low concentrations and lack of suitable spectral signatures for nitroaromatic explosives. Therefore, there remains a need for a reliable method of remote detection of buried minefields and/or antipersonnel minefields.
The present invention is directed to a method for the remote detection of trace contaminants in a target area, comprising applying to the target area sensor particles capable of preconcentrating the trace contaminant and having comprising a contaminant-sensitive fluorescent compound with optical emission that is sensitive to the presence of the trace contaminant; and detecting the optical emission of the contaminant-sensitive fluorescent compound with a detection means to determine the amount of trace contaminant present in the target area. The method further comprises adding a contaminant-insensitive fluorescent compound with optical emission that is insensitive to the presence of the trace contaminant to the sensor particles prior to applying the sensor particles to the target area. The contaminant-insensitive fluorescent compound provides an internal reference whereby the optical emission of the contaminant-sensitive fluorescent compound can be compared to the optical emission of the contaminant-insensitive fluorescent compound to determine the amount of trace contaminant present in the target area. The method further comprises exposing the target area to a mobile phase to facilitate the uptake of the trace contaminant by the sensor particles. The fluorescence detection can be done locally or remotely. Furthermore, the detection means can be a spectroscopic or imaging detector.